The invention relates to a multi-output DC/DC converter, comprising inductive electrical energy storage means, switching means and control means, wherein the control means are arranged for selectively operating the switching means for transferring an amount of electrical energy from the energy storage means to an output of the DC/DC converter providing an output voltage in accordance with a switching sequence based on comparing, by the control means, of the output voltage of each output with an associated reference voltage.
A DC/DC converter of this type is know from U.S. Pat. No. 5,751,139.
In this known converter, if the output voltages of a plurality of outputs of the converter drop below their associated reference or threshold voltages, the thresholds determine which output receives electrical energy. That is, if the output voltage of a first or priority output drops below its reference voltage, this particular output always receives priority for service, i.e. transfer of electrical energy. In the event that the output voltage of the first output is above its reference voltage, a second output receives priority for service. If the output voltages of the first output and the second output are above their reference voltages, a third output receives service, et cetera.
This type of control sequence has the inherent disadvantage that in case the first output is heavily loaded, such that its output voltage does not reach its reference voltage, the second, third and other outputs of the known multi-output DC/DC converter will not receive any service, such that the output voltages of these outputs eventually will drop to zero.
Accordingly, it is an object of the present invention to propose an improved control sequence for a multi-output DC/DC converter of the type indicated in the preamble preventing an output voltage to drop to zero.
This object is solved in that the control means are arranged for operatively controlling the switching means for each output in accordance with an output individual switching cycle, and wherein the switching sequence is comprised of the output individual switching cycles for transferring electrical energy to said outputs of said multi-output DC/DC converter in a predetermined order of priority.
In accordance with the present invention, the outputs of the multi-output DC/DC converter are each serviced by a switching cycle individual to a particular output, and outputs which require the transfer of electrical energy are serviced in accordance with a mutual order of priority.
That is, in accordance with the present invention, outputs which require the transfer of electrical energy in order to update their output voltage, will receive service also in the case that the output voltage of a particular output remains below its reference voltage despite the transfer of electrical energy to this output. With the present invention it is effectively avoided that the output voltage of an output drops to zero, due to lack of service, i.e. lack of transfer of electrical energy.
In a further embodiment of the DC/DC converter according to the invention, the selection sequence comprises a wait cycle wherein no energy is transferred to an output of the multi-output DC/DC converter. In this wait cycle, typically no energy is stored in the energy storage means. The wait cycle provides a very efficient control of the output voltages of the outputs at a specified voltage level in case of varying loads, for example.
In a yet further embodiment of the invention, starting from the wait cycle, the outputs of the multi-output DC/DC converter are serviced in a predetermined order of priority. That is, if a plurality of outputs require the transfer of electrical energy while the converter is in its wait cycle, the respective outputs are serviced in accordance with a priority scheme. This priority scheme can be set such that the output which is most heavily loaded receives priority in the transfer of energy.
The improvement according to the present invention is applicable to control means which are arranged to operate the multi-output DC/DC converter either in one or both Pulse Width Modulation (PWM) mode and Pulse Frequency Modulation (PFM) mode switching.
The invention may be practised with a plurality of DC/DC converter designs, such as but not limited to, at least one of a group including multi-output DC/DC up converters, multi-output DC/DC down converters, multi-output DC/DC up/down converters, multi-output DC/DC inverting converters, multi-output DC/DC converters with positive and negative output, and multi-output DC/DC up/down converters with multiple positive and negative outputs.
The invention also relates to a power supply comprising a multi-output DC/DC converter as disclosed above, arranged for receiving an input voltage at input terminals and for providing controlled output voltages at multiple output terminals.
The DC/DC converter according to the invention is of particular advantage if applied in an electronic appliance, such as, but not limited to, a portable electronic appliance.